Amiga 3000 memory is installed in "banks" or groups of 8 chips per bank. For instance, if you installed just 4 megs (8 chips) the first zip would go into the first socked, then you would skip 3 sockets and plug in the next zip, then you would skip 3 more sockets and plug in the next zip, and so on. The zip ram is not plugged into the zip sockets in a row, like the DRAMs are.
